1. Field of the Invention
This invention relates to a conjugated diene series rubber composition having improved strength at breakage, abrasion resistance and low heat build-up after vulcanization.
2. Description of the Related Art
Lately, the demand on safeness and low fuel consumption of automobiles becomes more severer and hence the rubber material for automobile tire is strongly demanded to have an abrasion resistance in addition to the safeness and low fuel consumption. Heretofore, the rubber composition containing styrene-butadiene copolymer rubber obtained by emulsion polymerization process (E-SBR) has widely been used as a tread for the tire owing to the excellent abrasion resistance. However, the rubber composition containing E-SBR is large in the energy loss and is apt to generate heat, so that it is unsuitable for treads directing to the low fuel consumption.
In order to solve this problem, there are used rubber compositions containing styrene-butadiene copolymer rubber obtained by solution polymerization process (S-SBR). S-SBR is obtained by copolymerizing butadiene with styrene in a hydrocarbon solvent in the presence of an organolithium initiator and has a narrow molecular weight distribution. That is, S-SBR does not contain low molecular weight component as compared with E-SBR and is small in the hystresis loss, so that it is suitable for the tread directing to the low fuel consumption.
Furthermore, as disclosed in Japanese Patent Application Publication No. 44-4996, Japanese Patent laid open No. 57-205414 and U.S. Pat. No. 3,956,232, terminal-modified S-SBR can be obtained by utilizing an activity of terminal group in S-SBR after the polymerization and reacting it with a halogenated tin compound or an alkenyl tin compound. When such a terminal-modified S-SBR is compounded with carbon black and the like, the resulting rubber composition provides considerably low heat build-up or low fuel consumption.
However, such S-SBRs are low in the heat build-up or fuel consumption but are poor in the strength and abrasion resistance as compared with E-SBR as a rubber composition, so that it is difficult to synthesize S-SBR simultaneously satisfying low fuel consumption and excellent abrasion resistance.